1. Field of the Invention
The present invention relates generally to a mounting device for supporting a power unit including an engine of an automotive vehicle. The mounting device is adapted for damping transmission of vibration over a wide frequency range. More particularly, the invention is directed to a mounting device having improved geometry which provides easy installation and high heat resistance.
2. Description of the Prior Art
Japanese Utility Model First Publication No. 63-123845 discloses a conventional power unit mounting device for an automotive vehicle which is designed to support a power unit on a vehicle chassis. This power unit mounting device comprises an elastic supporting member defining a main working chamber, a diaphragm defining an auxiliary working chamber, and an orifice passage fluidly communicating between the main and auxiliary working chambers. The main and auxiliary working chambers are respectively variable of volume due to elastic distortion of the elastic supporting member and the diaphragm. By changing a cross-sectional area of the orifice passage according to frequency of input vibration from the power unit, vibration may be attenuated in a number of different frequency ranges.
With this arrangement, when input vibration falls in a high frequency engine idle range, increasing the cross-sectional area of the orifice passage causes the mounting device to assume a lower dynamic spring constant suitable for absorbing the high frequency vibration, while when the input vibration fails in a low frequency engine shake range with high amplitude, decreasing the cross-sectional area of the orifice passage provides a high dynamic spring constant exhibiting high damping characteristics.
However, the above prior art power unit mounting device encounters a drawback in that an actuator which serves to vary a cross-sectional area of the orifice passage is arranged outside the mounting device and thus the device geometry makes installation on different types of vehicles difficult. Additionally, the mounting device is subject to radiant heat from an engine and/or an exhaust pipe, resulting in heat resistance being deteriorated.